Calculation of impedances is great but nothing takes the place of actual
measurement.
73
Bob, K4TAX
----- Original Message -----
From: "Denton" <denton@oregontrail.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Friday, April 11, 2008 8:28 AM
Subject: Re: [TenTec] Ten Tec 238A settings?
>I use Eznec to calculate impendences....and also have tried a 1:1 and a 2:1
> balun using same 600 ohm feeders...but nothing gives me as close a match
> as
> the 4:1 balun.
> ----- Original Message -----
> From: "Bob McGraw - K4TAX" <RMcGraw@Blomand.net>
> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
> Sent: Friday, April 11, 2008 5:08 AM
> Subject: Re: [TenTec] Ten Tec 238A settings?
>
>
>> Large variations in tuner settings from one end of 80M to the other end
>> is
>> normal. This is about typical of all tuners as the ratio of bandwidth to
>> frequency is greater on the lower frequency bands than on higher
>> bands/frequencies. I really haven't found a band or frequency or
>> reasonable
>> antenna below 30 MHz that the 238 tuner would not handle. {I've not tried
>> to
>> load a coat hanger. hi hi}
>>
>> I do have a chart based on settings for all bands and several settings
>> vs.
>> frequency for each band, and for two different antennas. This makes for
>> quick tune-up when changing antennas or bands. I'll be glad to share
>> that
>> but it most likely would apply only to my antenna configurations, those
>> being a 1/2 wave for 160M fed with balanced line and a 1/2 wave for 75M
>> fed
>> with coax.
>>
>> I do not suggest using a 4:1 balun for your configuration but a 1:1
>> current
>> balun. These are typically less lossy as you are not matching the feed
>> line
>> Z but the antenna load Z which is likely closer to 35 to 100 ohms or
>> less.
>> If you have an Antenna Analyzer measure the Z at the balun coax terminal.
>> You'll likely find that it is 10 to 25 ohms. This being the case then a
>> 1:1
>> balun would be more nearly correct as the load with that configuration
>> would
>> be 40 to 75 ohms. Again, a better match for your coax between the balun
>> and
>> the tuner.
>>
>> For whatever reason, using balanced line of some 400 to 600 ohms, hams
>> typically believe they should match the feedline Z. In actuality the
>> feedline is more correctly reflecting the antenna feed impedance. And is
>> some cases, acting like a transmission line transformer.
>>
>> Here is a case where a 4:1 balun is accurately used. The old fashion
>> folded
>> dipole made of twin lead. The feed Z of a 1/2 wave folded dipole where
>> the
>> top and bottom conductors are of equal size is nominally 300 ohms when
>> greater than 1/4 wave above ground. Add an electrical 1/2 wave of
>> feedline
>> and one has an antenna with a feed impedance at the transmitter of about
>> 300
>> ohms. Use a 4:1 balun and the transmitter feed is 75 ohms showing a SWR
>> of
>> 1.5:1 . Drop the antenna down to less than 1/4 wave and the feed Z will
>> drop toward 200 ohms which then with a 4:1 balun the feed point for the
>> transmitter is now approaching 50 ohms.
>>
>> 73
>> Bob, K4TAX
>>
>>
>> ----- Original Message -----
>> From: "Denton" <denton@oregontrail.net>
>> To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
>> Sent: Friday, April 11, 2008 12:28 AM
>> Subject: [TenTec] Ten Tec 238A settings?
>>
>>
>>>I have a horizital loop up about 30' that has about 240' of wire in
>>>roughly
>>> a trapazoid shape....have found that by using a certain length of 600
>>> ohm
>>> feeders with a 4 to 1 balun, I have swr below 3.5 to 1 or below on all
>>> bands
>>> from 80 thru 10 meters, as measured at the balun's input...with the
>>> exception of 17 and 60 meters. I am also using about 20 ft of good
>>> quality
>>> coax to the shack with a TT 238A tuner to take care of the minor swr on
>>> the
>>> system.
>>> I notice that on 75 and 80 meters there is a large variation in tuner
>>> settings from one end of the band to the other....is this typical of TT
>>> tuners and L networks in general?
>>> It appears to be a decent antenna system....if I can hear them, can work
>>> them.
>>> I have also verified the antenna's effiectiveness by also using it with
>>> a
>>> link coupled transmatch...by extending the 600 ohm feeders and running a
>>> short stubb of 400 ohm line to the shack.
>>> TT's L network gives me a much broader matching range, otherwise would
>>> just
>>> use the balanced transmatch.
>>>
>>>
>>> _______________________________________________
>>> TenTec mailing list
>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>
>>
>>
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>>
>>
>
>
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